Importance

Loading Importance Indicators...

Abstract

A refining method of decarburizing a molten steel containing a large quantity of chromium, which can be completed in a shorter period, and therefore, with reduced consumption of Ar gas, and with safety of operation. A mixed gas of O.sub.2 and Ar is blown into a molten steel in a refining vessel through a tuyere at the bottom of the vessel under atmospheric pressure, and when the C-concentration becomes to such a low level as 0.15% (by weight) or less, vacuum suction is applied to reduce the pressure to 150-200 Torr, and only Ar gas is blown. At the change of the refining conditions from atmospheric to vacuum or during the vacuum refining a reducing agent such as ferrosilicon is added to the molten steel to reduce Cr-oxides for recovery. Even if the amount of the reducing agent is less than that necessary for reducing all the Cr oxides, majority of Cr can be recovered. If an excess amount is used, a steel of low nitrogen in addition to low carbon is obtained. Whole or a portion of Ar can be replaced with N.sub.2. Refining may be carried out economically when compared with conventional refining method such as AOD process by reducing At-consumption. It is possible to obtain a steel containing desired nitrogen by changing the blown gas from N.sub.2 to Ar and choosing the timing of changing depending on the desired N-concentration.

Loading the Abstract Image...

First Claim